Performance of any particular garment will depend on a number of factors, including, but not limited to, design, seams, closures, accessories, duration of use, maintenance of garment, and proper handling. (W.L. Gore & Associates Inc. photo)

Selecting Chemical-Protective Clothing

Each end-use situation must be evaluated for its particular risks.

Choosing the right chemical-protective clothing can be difficult due to a lack of standards and insufficient data. It has been common to choose chemical-protective clothing based on the A, B, and C levels defined by the EPA. While these definitions provide guidelines and a framework for discussing PPE, the descriptive narrative in these levels does not identify the minimum performance criteria required to assure that the wearer is adequately protected from any specific hazards.

The NFPA Approach
Choosing the correct protective clothing requires a clear understanding of what the garment is expected to do and why it is being worn. This practical and simple approach was used by the National Fire Protection Association (NFPA) to establish performance-oriented protective clothing standards as follows:

  • NFPA 1991       Vapor-Protective Ensembles for Hazardous Materials Emergencies
  • NFPA 1992       Liquid Splash-Protective Ensembles and Clothing for Hazardous Materials Emergencies

These standards address full ensemble performance. Each standard sets minimum levels of performance for protection provided by the overall ensemble, garment material, seams, closures, and other components. These criteria have been written with the hazardous chemical emergency response team in mind, but they can apply to a number of other protective clothing applications, as well.

Because the NFPA standards define performance levels instead of design levels, they are more appropriate for selecting types of protective ensembles and clothing than the A, B, C, or D levels from EPA. The terminology from these standards can be related, as the comparison in the following table shows:

 

When Vapor Protection is Needed
When you need vapor protection, it is appropriate to choose a certified vapor-protective ensemble when the capability to protect against a specific chemical is based on permeation data (ASTM F739). Permeation is the process by which a chemical moves through material on a molecular level. NFPA 1991 associates vapor-tight integrity and permeation data (ASTM F739) with vapor protection. Therefore, vapor-protective ensembles compliant with NFPA 1991 are suitable for this purpose.

When Liquid Splash Protection is Needed
When you need liquid splash protection, but do not need vapor protection, it is appropriate to choose a certified liquid splash protective ensemble that meets NFPA 1992. These protective ensembles are selected for their capability to protect against a specific chemical based on penetration data (ASTM F903). Penetration is the bulk flow of a liquid chemical through the material, seams, or suit closures. NFPA 1992 associates liquid-tight integrity and penetration data (ASTM F903) with liquid splash protection. Because clothing of this type is designed to protect the wearer from liquid contact, but allows exposure to vapors, permeation data is inappropriate for judging material performance for this level of protection.

In addition, the overall ensemble also must demonstrate liquid-tight integrity. NFPA 1992 provides test methods and criteria for making this assessment. Organizations such as the Safety Equipment Institute (SEI) and Underwriters Laboratories (UL) will certify complete protective clothing ensembles that meet the NFPA standards.

Other test methods are often used to describe the liquid resistance of materials. However, the choice of liquid splash-protective clothing should be based on the results of penetration testing that has been performed in accordance with the procedures in ASTM F903, Procedure C. These criteria provide a truer evaluation of liquid barrier performance.

When Both Vapor and Liquid Splash Protection Are Needed
When you need both vapor and liquid splash protection, it is appropriate to choose a certified vapor-protective ensemble compliant with NFPA 1991 because, by definition, vapor-protective ensembles also provide liquid splash protection. Never use liquid splash-protective clothing in vapor exposure situations, even if the material offers acceptable resistance to chemical permeation, because these suits lack overall vapor-tight integrity. Penetration data is inappropriate for judging material performance for this level of protection.

Penetration Resistance
Penetration is the bulk flow of a liquid through porous materials, seams, closures, and pinholes or other imperfections in a protective clothing ensemble. Penetration may occur from chemical deterioration of the materials, which leads to a liquid passing through the material.

Measurement of Penetration Resistance
The penetration test as specified in National Fire Protection Association (NFPA) 19921 measures the resistance of protective clothing materials to penetration by liquids using a one-hour, one-sided liquid exposure to the normal outside material surface. The test is conducted at atmospheric pressure and room temperature. During the sixth minute, the test is conducted at 2 psig to simulate the pressure from a burst pipe. Liquid penetration is detected visually at the end of the test. Penetration results are recorded as either "PASS" or "FAIL."

Heat Stress is Also a Serious Hazard
Heat stress is a serious hazard to wearers of chemical protective clothing. In some cases, heat stress may be even more dangerous than the chemical hazard itself. To release heat, your body sweats, and when the sweat evaporates, your body is cooled.

Chemical-protective clothing limits sweat evaporation. Liquid splash garments based on continuous film materials, such as vinyl or rubber, have one function for the wearer—protection against accidental contact with liquid chemicals. Vapor-protective ensembles prevent sweat evaporation altogether. None of these types of chemical-protective clothing provide relief from heat stress.

Solution to Heat Stress
The ideal product solution is one that offers chemical splash protection per NFPA 1992 while allowing sweat vapor to escape.

Look for a garment that offers protection against chemicals that are listed in the NFPA 1992 standard, as well as other chemicals meeting the NFPA 1992 guidelines—the chemicals that pose no threat in a vapor state or chemicals that have vapor pressures low enough (< 5 mm Hg at 25° C) not to pose a vapor threat.

It may be appropriate to use such fabric when you need protection against chemicals that are outside NFPA 1992 guidelines and it has been determined that a certain level of vapor exposure is acceptable. Be sure to consult with the manufacturer of your chosen protective garments.

NFPA standards were developed for emergency situations, but not all exposures to hazardous chemicals are emergencies. Each end-use situation must be evaluated for its particular risks.

A chemical-by-chemical determination alone is not always sufficient to capture the various situations where chemical-protective clothing is used. Additional circumstances such as quantity and temperature, at least, need to be considered. Always consult a trained professional in safety or industrial hygiene when making this determination.

Safety Considerations
Before determining fitness for use in any chemical application, consult a trained professional in safety or industrial hygiene. It is important to understand that any chemical-protective clothing does not provide protection from all chemicals or in all conditions, and that technical information typically documents laboratory performance under laboratory conditions. Testing results are often for fabric only. Performance of any particular garment will depend on a number of factors, including, but not limited to, design, seams, closures, accessories, duration of use, maintenance of garment, and proper handling.

Reference
1. Penetration test procedures as specified in National Fire Protection Association (NFPA) 1992—Standard on Liquid Splash-Protective Ensembles and Clothing for Hazardous Materials Emergencies. These procedures are identical to those in ASTM F903, Procedure C.

This article originally appeared in the August 2018 issue of Occupational Health & Safety.

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